Overgrow

Overgrow (Japanese: しんりょくFresh Greenery) is an ability introduced in Generation I. All of the Pokémon that have this ability are the Grass-typeStarter Pokémon from all regions, as well as Pansage and Simisage though only obtained in Dream World. In total, 17 Pokémon have this ability. Overgrow increases the holder's Grass-type moves' damage, making them do 150% damage. However, this only happens when the Pokémon has 30% of its original HP remaining. Overgrow has no effect outside of battle.